The present invention is directed a device for sensing the position of an edge of a product, as well as to a method for sensing the position of an edge of a product.
During the process of printing sheets, in particular in a sheet-fed offset press, the sheets are supplied to the press from a sheet stack. When a single sheet is fed to the printing press, known methods heretofore provide for the sheet to be laterally aligned at the feeder along a guide edge. However, it is also possible for the sheet to be laterally aligned by actuator-driven displacement of the front sheet edge on the cylinder, thus during conveyance of the sheet. Such actuator-driven displacement is known, for example, from the German Application DE 196 18 030 and related U.S. Pat. No. 6,264,196, which is hereby incorporated by reference herein. In response to the actuator-driven displacement, the sheet is guided to a defined setpoint position, the actual position of the sheet being detected by sensors.
To ensure exact alignment of the sheet, the actual position of the sheet edge must be precisely determined. A device for sensing and controlling the edge position of a continuous web is already known from the German Application DE 36 37 874. When working with this device, a web is irradiated by an illuminating device that extends over a planar area. The light beams striking the web are reflected from there in accordance with the laws of reflection and fed to an electro-optical image sensor. The electro-optical image sensor scans a strip on the web by sequential lines, the strip also encompassing a partial area situated outside of the web. In this way, the width of the area situated outside of the web can be determined and, from this, in turn, the position of the web. However, this method can only be applied when the material web used is a material web that is sufficiently reflective in accordance with the laws of reflection. This is particularly not the case when working with transparent films.
From the German Application DE 101 36 871, a device is known for sensing the position of an edge of a sheet that is fed to a printing press. In this case, an opto-electronic measuring device is used, which is oriented orthogonally to the conveyance direction of the sheet.
The measuring device is mounted above the feedboard and has reflecting arrays which are able to detect a reflected beam. To enable problematic sheets to be detected, in particular transparent or high-gloss materials, the surface of the feedboard is additionally provided with contrast-enhancing means. To this end, the feedboard is specially finished in one partial area, in particular highly polished, chromium-plated, or provided with a reflective layer. However, the drawback when working with this device is that it is no longer possible to distinguish the materials themselves from the contrast-enhancing layer when the sheets to be measured have surface properties which correspond or nearly match those of a highly polished or chromed surface.